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Last week was a big one for those who like their T-rays. The spy-beam technology has been used to view murals hidden beneath inches of plaster, and has also been linked to metamaterials - the stuff from which invisible sheds could be made.

In the first development, art boffins from Paris's famous Louvre museum - collaborating with American colleagues - announced they had used T-ray scanners to "detect coloured paints and a graphite drawing of a butterfly through 4mm of plaster". The technique could apparently be used in many similar feats.

"In France alone, you have 100,000 churches," said Professor Gèrard Mourou of the Laboratoire d'Optique Appliquèe, one of the team behind the T-ray plaster probe.

"In many of these places, we know there is something hidden. It has already been written about. This is a quick way to find it."

Mourou noted that a famous Leonardo da Vinci painting, "The Battle of Anghiari", is thought to lie hidden behind a fresco at the Palazzo Vecchio in Florence. The culture-loving electronics prof reckoned that T-ray imaging would allow the world to see da Vinci's masterpiece once again without damaging the overlying art.

Meanwhile, other T-ray boffins from Blighty and Spain were working on a way to control and guide the tricky spy beams, which is difficult using ordinary substances such as metal.

"T-rays have the potential to revolutionise security screening for dangerous materials such as explosives," said Dr Stefan Maier of Imperial College.

"Until now it hasn't been possible to exert the necessary control and guidance... for it to have been usable in real world applications. We have shown with our material that it is possible to tightly guide T-rays along a metal sheet, possibly even around corners, increasing their suitability for a wide range of situations."

T-rays get their name from their terahertz frequencies, lying between microwave RF and the far infrared - or as some say, between electronics and optics.

It could be good to use T-rays rather than X-rays for security, as this would allow the everyday scanning of people without upping their cancer risk. Quite apart from the possible speeding-up of airport queues, this would also allow the entry checks at secret spy agencies to finally live up to their movie image.

Brit warboffinry spinoff Qinetiq hopes so, anyway, and has managed to sell some T-ray gear to the American homeland-security people.

Qinetiq prefers the term "millimetre wave" to "T-ray", but one man's millimetre-wave radar is another's T-ray spy beam. Qinetiq's gear is passive, however: it scans the T-rays naturally emitted by human bodies and using automated software to check for non-emitting materials like metal, plastic, or ceramics.

If the easily-usable active gear has to wait for metamaterials from the lab at Imperial, though, it might be a while coming. The days of the through-clothes spy spectacle rig are not upon us quite yet, though the through-clothes airport scanner has already been trialled. But when the proper new metamaterial gear comes in, presumably the only place to hide will be in one's invisible shed. ®